Time and room: 10:15, lecture hall IAPAbstract: Among various platforms for quantum computing and simulations, trapped neutral atoms offer unique advantages of long coherence time, scaling and excellent control of the interaction strength over 12 orders. However there are still several primary challenges to be solved. In this talk, I will present our recent experimental efforts towards two problems. One is extending single qubit coherence time using magic intensity dipole trap. The other is entangling two heteronuclear single atoms using Rydberg blockade for low crosstalk qubit measurement with a few µm qubit spacing.

Time and room: 17:15, lecture hall IAPAbstract: We are developing a comprehensive set of experimental tools, based on ion-trapping and photonic technologies, that enable controlled generation, storage, transmission, and conversion of single photonic quantum bits, thereby integrating single photons and single atoms into a quantum network. Specifically, we implemented a programmable atom-photon interface, employing the controlled quantum interaction between a single trapped 40Ca+ ion and single photons [1,2]. Depending on its mode of operation, the interface serves as a bi-directional atom-photon quantum state converter (receiver and sender), as a source of entangled atom-photon states (entangler), or as a quantum frequency converter of single photons [3,4] (converter). It lends itself particularly to integrating ions with single photons or entangled photon pairs from spontaneous parametric down-conversion (SPDC) sources [5,6]. As an experimental application of the receiver mode, we demonstrate the transfer of entanglement from an SPDC photon pair to atom-photon pairs with high fidelity [7]. It is realized by heralded absorption and storage of a single photonic qubit in a single ion. We extend our quantum network toolbox into the telecom regime by quantum frequency conversion of ion-resonant single photons [9], and by implementing telecom-heralded single-photon absorption [5]. In addition, we observe signatures of entanglement between the ion and a single telecom photon. This is obtained after controlled emission of a single photon at 854 nm and its polarization-preserving frequency conversion into the telecom band, by difference-frequency generation in a nonlinear waveguide.

Invited speaker: Sandro WimbergerAffiliation: Università di Parma Title: Discrete-time walks of a Bose-Einstein condensate in momentum spaceTime and room: 09:15, Seminar room I, HISKP 1.021Abstract: Each step in a discrete-time quantum walk is typically understood to have two basic components: a „coin-toss“ which produces a random superposition of two states, and a displacement which moves each component of the superposition by different amounts. Here we report on the experimental realization of a walk in momentum space with a spinor Bose-Einstein condensate (BEC) subject to a quantum ratchet realized with a pulsed, off-resonant optical lattice. By an appropriate choice of the lattice detuning, we show how the atomic momentum can be entangled with the internal spin states of the atoms. For the coin-toss, we propose to use a microwave pulse to mix these internal states. We present first experimental results of such a quantum walk based on a new type of ratchet, and through a series of simulations, demonstrate how our system can allow for the investigation of possible biases and classical-to-quantum dynamics in the presence of natural and engineered noise. Moreover, the same setup offers the possibility to realize classical random walks by applying a random sequence of intensities and phases of the time-dependent lattice chosen according to a given probability distribution. This distribution converts on average into the final momentum distribution of the atoms. In particular, it is shown that a power-law distribution for the intensities results in a classical Lévy walk in momentum space. Finally, we propose another implementation of a BEC quantum walk in reciprocal or quasimomentum space with exciting possibilities to investigate the effects of long-range quantum correlations induced by atom-atom interactions.

Invited speaker: Günter HuberAffiliation: Universität HamburgTitle: Semiconductor Laser Pumped Rare Earth Ion Doped Solid-state Lasers
in the Visible and Near Infrared Spectral RegionTime and room: 17:15, lecture hall IAPAbstract:The talk reviews the basic concepts of advanced highly efficient rare earth ion doped
solid-state lasers based on laser ions such as Yb3+, Tm3+, Er3+, Pr3+, and Tb3+ which
have opened new prospects for laser applications at various wavelengths and power
regimes. The main emphasis is placed on the interplay between materials aspects and
most relevant spectroscopic as well as laser related properties in the search for new
solid-state laser systems.
For the near infrared spectral region Yb3+-doped laser crystals feature very high
efficiencies and reduced heat generation due to small Stokes-losses between pump and
laser photons. In particular, Yb3+:Lu2O3 possesses high thermal conductivity and have
been operated at record slope efficiencies of 80% in continuous wave operation and at
more than 100 W of average power in the mode-locked sub-ps operation regime. Laser
diode pumped, highly efficient 2-μm Tm3+- and 3-μm Er3+-lasers with special interest
for medical applications are based on interionic interactions of Tm3+ and Er3+ laser ions,
respectively.
Breakthroughs regarding efficient visible coherent light generation have been achieved
with Pr3+- and Tb3+-lasers operating in the green, orange, and red spectral region under
blue semiconductor laser pumping. Here both, the development of blue semiconductor
pump lasers and the use of suitable short wavelength hosts with minimized excited state
absorption of the laser ions contributed to major achievements.
The functionality of laser crystals can be further increased by direct micro-structuring of
bulk crystals with ultrafast laser pulses yielding for instance efficient waveguide lasers
with diffraction limited, fundamental modes in the near infrared and visible spectral
region. This simple direct light writing technique is also suitable for the fabrication of
more complex structures for integrated optics in single crystalline dielectrics.